Grinding machine with wheel surface position indicator



Oct. 27, 1953 I R. D. GARDNER GRINDING MACHINE WITH WHEEL SURFACE POSITION INDICATOR 4 Sheets-Sheet 1 Filed D80.

Nvsr'u-ro PRGIJDH D.Gardner Cu, 4,- ,MW ((14,

I OT'TOJNBY/ Oct. 27, 1953 R. DQGARDNER 2,656,653

GRINDING MACHINE WITH WHEEL SURFACE POSITION INDICATOR Filed Dec. 16, 1950 4 Sheets-Sheet .2

2 A Ra lra zrdner CJI QmE: 7/

Oct. 27,1953 D. GARDNER GRINDING MACHINE WITH WHEEL SURFACE POSITION INDICATOR 4 Sheets-Sheet 3 Filed Dec.

AMPLIFIER M A z a w W.

Ralyh D. Gardner ca I/O-$",,MMCA

Patented Oct. 27, 1953 GRINDING MACHINE WITH WHEEL SUR- FACE POSITION INDICATOR Ralph D. Gardner, Roscoe, Ill., assignor to Gardner Machine Company, South Beloit, 111., a corporation of Illinois Application December 16, 1950, Serial No. 201,081

12 Claims.

1 The present invention relates generally to the field of machine tools and more specifically to a novel grinding machine having means whereby one or more of the abrading elements therein may be positioned with nicety and precision.

The invention finds particular, but by no means exclusive, utility when embodied in a machine having opposed abrasive wheels adapted to operate simultaneously on both sides of the Work. Such a machine is disclosed, for example, in United States Patent No. 2,142,444, issued January 3, 1939, to Donald R. Hall.

In a grinding machine, the work-engaging surface of the abrasive wheel tends to change position due to wear which occurs as the machine is operated. Where work is being ground to a predetermined dimension, periodic adjustment of the position of the abrasive wheel is necessary if such dimension is to be maintained.

Since the work-engaging surface might not wear uniformly, the usual practice is to dress such surface prior to repositioning the wheel. After the dressing operation, if such be performed, or after a given period of use in the event the wheel is not dressed, a predetermined repositioning adjustment is imparted to the wheel. Such adjustment is predicated upon an approximation of the amount of material removed from the work-engaging surface of the grinding wheel and positions the latter where the operator thinks it should be. In ordinary grinding machines, this sort of adjustment is sufficiently accurate for certain classes of work in which a high degree of precision is not required.

In a machine of the character disclosed in Hall Patent No. 2,142,444, where the opposed faces of a pair of abrasive wheels operate simultaneously on both sides of the work, a number of difliculties are apt to be encountered when repositioning adjustment of the wheels is effected in the manner outlined above. Moreover, when the abrasive wheels of such a machine are closely spaced for precision grinding of piston rings or other relatively thin workpieces which are moved in a procession along a pair of spaced apart guide bars located between the wheels, conventional wheel positioning techniques aggravate such difficulties. At the outset, it will be observed that a variable which tends to upset the accuracy of a fixed compensating adjustment for each wheel is injected due to the improbability that the amount of wear on the grinding face of one wheel will be identical with the amount of wear on the grinding face of the other wheel. Dressing of the grinding faces not only fails to eliminate this variable, but, in addition, the dressing operation is apt to inject still another variable due to the fact that the dressing tool will itself experience an appreciable amount of wear unless it is a diamond. Consequently, when the wheels are repositioned after the dressing operation by the application of a fixed adjustment based on an approximation of wear, there is a definite possibility that improper spacing between the two grinding faces will occur. There is also a definite possibility that the wheel spacing will be unbalanced or off center with respect to the guide bars which extend between the opposed grinding faces. In other words, the guide bars will be located closer to one of the opposed grinding faces than to the other. Since grinding machines of the foregoing character usually have their wheels enclosed, the operator is unable to observe the wheels when making his compensating adjustments for positioning them. Under such circumstances, the grinding face of one of the wheels is apt to make contact with the guide bars, resulting in spoilage of the latter, spillage of the workpieces, and considerable down time of the grinding machine.

One object of the invention is to provide a grinding machine including means for apprising the operator as to the arrival of the work-em gaging surface of the abrasive element or elements at a preselected, predetermined position during adjustment of such element or elements.

Another object is to provide a grinding machine having means for precisely determining the extent to which material has been removed from the work-engaging surface of one or more of its abrasive elements due either to Wear or to a dressing operation.

A further object of the invention is to provide a grinding machine of the character set forth and wherein the abrasive element or elements can be readily positioned for dressing and repositioned with nicety and precision after dressing, permitting accurate maintenance of a predetermined dimension in the work.

Still another object is to provide a novel wheel surface position indicator susceptible of use in effecting repositioning of one or more of the abrasive elements or of precisely controlling infeed operations of these elements.

Other objects and advantages of the invention will become apparent as the following description proceeds, taken in connection with the accompanying drawings, wherein:

Figure 1 is a front elevational view of an illusmachine of Fig. 1 and taken approximately along the longitudinal metal plane of the machine.

Fig. 4 is an enlarged fragmentary vertical sectional view taken in the plane of the line 44 in Fig. 1 and detailing a'portion of the mdicator means.

Fig. 5 is an enlarged fragmentary broken sectional view through a portion or the indicator means, such view being taken in the plane of the line 5-5 in Fig. 4.

Figs. 6 and 7 are enlarged fragmentary horizontal sectional views taken through the righthand half or the machine of Fig. 1 and in the plane of th'e'line 6-6 in Fig. 3.

Fig. 8 is an enlarged fragmentary vertical sectibnal view taken through a portion of the mechanism shown in Fig. 7 and in the plane of the line 88.

While the inventionis susceptible of various modifications and alternative constructions, a preferred embodiment has been shown in the drawings and will bed'esc'ribed below in considera'bledeta'il. It'should be understood, however, that there is no intention to lir'nit the'invention tothe specific form disclosed, but on the contrary, the intention is to cover 'all'modifications and alternativeconstructions falling within the spirit and scope of the invention as expressed in the appended claims.

Referring more specifically to Fig. 1, the invention is there shownembodied in an illustrativ'e grinding machine 29 of the general type disclosed in Hall Patent No; 2,142,444, referred to above. Themachiue 2e comprises a box-like base 2! of substantially rectangular shape, together with a pair "of beds 22 fixed in spaced apart relation on the top of the base. Each of theb'eds 22 is of hollow, box-like form and is provided with a channel 24 in its to surface defining a pair of ways 25 running longitudinally of the base 2] (see Fig. 2). Disposed within corresponding ones of the channels 2 4 and supported for relative sliding movement on the ways '25 are a pair 'of slides '26 each of which carries one of 'apair of substantially i'dentical' grinding heads 28. In view' of their similarity, a de- 'scription of one of th'eheads '28 will sufii'ce for both. Thus there'is jou'rnaled in suitable bearings within the head 28 a'driving spindle '29 terminating at it 'inner' end in a supporting disk it "and backing plate 3!, the latter having fixed thereto an abrasive element in the form of a grinding disk 32. Together, the plate '31 and disk 32 "constitute anabrasive wheel 34 (see Fig. 3). The wheel '34 is rotated by suitable means such as motor 35 which 'transm-itspower to the end of the "spindle 2%} remote from the Wheel as by means ofpulleys 36, 38 and belts 39. In the machine 29-, these members are enclosed by means of ,j'a protective hood 4!). The latter may be utilized to support a "coolant bonnet 4| which is adapted to introduce fluid coolant into an axial passage (not shown) 'in the spindle '29 which'cond'ucts it to the abrasive wheel 34.

Due to the fact that the structure just dcscri'b'ed is duplicated in the other grinding head accepts 28 and its associated drive means, it will be appreciated that the abrasive wheels 34 are located in closely spaced relation and define a grinding zone centrally oi the machine 20. In the present instance, both of the wheels 34 and the grinding zone are enclosed within a splashproof protective housing "42 of substantially rectangular form.

For the purpose of channeling a procession of workpieces, such as piston rings R, through the grinding zone, the machine 23 is equipped witha pair of vertically spaced guide bars 43 running substantially horizontally through the grinding zone and-along a diametrical axis (see Figs. 2' and 3). The guide bars 33 are adjustably fixed to the housing 42 and under normal operatingconditions are centered in the space between the grinding faces 64 of the abrasive wheels.

In order to position the abrasive wheels 34 with their grinding faces 44 in properly spaced relation for grinding the workpieces R to predetermined thickness, a suitable adjustable stop means is interposed between each of the grinding heads 28 and its associated supporting bed 22; Since this arrangement is substantially identical for each head, a description of the stop mechanism associated with the right-hand one of the grinding heads 28 (as shown in Figs. 1 and 3) will sufiice for both. Referring in particular to Fig. 3, it will be noted that the head 28 ha'sa relatively heavy boss 45 depending from its slide and extending'down into the'hollow region of the underlying bed. Fixed to the boss'45 as by means of screws 56 is a mounting pad 8 carrymg a hollow stop pin '49. The latter is formed with a generally fru'sto-conical recess complemental to tapered end '51 of an adjustable stop element '52. In this case, the element 52 happens to be integral with an adjusting screw 54 rigidly but adjustably supported within the bed 22. Controlled axial adjustment of the screw 54 and. the stop 52 relative to the bed 22 may be eiiected by rotating the screw within elongated nut 55 fixed to the bed 22. This is accomplished in the machine 28 as by meansof a worm wheel 58 spline'd or slidably keyed upon the screw '54 and disposed in meshing engagement with a worm '58. The latter is secured to a shaft 59 which projects through the'front wall of the bed 22 and carries adjusting hand wheel Gil in rigidly fixed relation with its projecting end (see Figs. 1 and 2).

The grinding head 28 may readily be urged in a direction tending to maintain abutting engagement'between the stops 49, 52 or in an opposite direction tending to separate the stops. This is accomplished in the present 'case as by means of a fluid actuator 6|. The latter comprises an air cylinder housed within the base 20 and having a piston rod 62 pivotally connected with the depending boss '45 through a rocker arm 64 pivoted on a pin'65 anchored to the machine base. The head 28 is normally biased in a direction tending to maintain the'stops 49, 52 in abutting relation. This may be achieved by suitable spring means associated with the actuator '6l or, alternatively, by making the actuator double acting and utilizing pressure fluid to create the biasing force. Since the structure thus far described is dupli cated for the other one of the grinding heads 28, it will be appreciated thatth'e abrasive wheels 34 may be moved into grinding position as indicated in dot-dash outline in Fig. 3 by bringing their associated stops 49, 52 into a condition'of direct abutting engagement as shown in Fig. 7

and thereuponadjusting each stop 52 through rotation of its corresponding hand wheel 66 in an appropriate direction.

After a given amount of operation, the grinding faces 44 of the wheels 34 must be dressed to restore their true contour. This is accomplished in the machine 26 by means of a dresser mechanism 66 which in the present instance happens to be mounted on the protective housing 42 enclosing the abrasive wheels. While the details of the dresser mechanism are unimportant for present purposes, it might be stated that the mechanism 66 includes a dressing tool which is adapted to take a relatively light out as it is moved across the grinding face 44 of each abrasive wheel. Since the thickness of the dressing tool is considerably greater than the distance between the abrasive wheels when in grinding position, it is necessary to retract the wheels 34 from each other to perform the dressing operation. Retraction of each of the wheels 34 may readily be effected by causing the grinding heads 28 to move away from each other and toward the ends of the base 2 I. This can be done in the machine 20 by controlling each of the actuators 6I in such a manner that its piston rod 62 moves toward the center of the machine.

Once retracted, the wheels 34 and their respective grinding heads 28 may be properly positioned for the dressing operation by interposing a spacer 68 of predetermined length between their adjacent stops 49, 52 and at the same time effecting abutting engagement between such parts by proper control of the actuators 6| and their associated biasing means (see Figs. 3 and 6) Each spacer 68 in thisinstance comprises a hollow boss 69 having a generally frusto-conical recess 56A at one end similar to the recess 56 and also complementary to the tapered end of the stop 52 against which it abuts. The boss 69 is carried by an arm I6 which, in turn, is rigid with another boss I2 mounted on a shaft I4. The spacer 68 is constrained to move with its associated grinding head 28, and also to rock in response to rocking of the shaft", by the use of a sleeve 15 which is fixed thereto. The sleeve I5 passes through an extension of the mounting pad 48 surrounding the shaft I4 and terminates at a collar I6 at its opposite end. The collar 16 is secured to the sleeve I5 as by means of a set screw I8, the inner end of which rides in a keyway I8 running longitudinally of the shaft I4. Thus, the, spacer 68 may be swung into and out of operative position simply by rocking the shaft I4 in the appropriate direction. For this purpose, there is fixed to the shaft I4 at one end thereof a depending crank arm 86 pivoted as by means of a pin 8| to the inner end of an operating plunger 82 which projects through the front wall of the bed 22 and terminates in an operating knob 84. Upon reference to Figs. 6 to 8, it will be perceived that when the plunger 82 and knob 84 are pulled outwardly, the spacer 68 is swung upwardly into operative position between the stops 49, 52. Conversely, when the plunger 82 and knob 84 are pushed in, the spacer 68 is swung downwardly into inoperative position. This structure is, of

.course, identical for each grinding head.

Provision is made in the grinding machine 26 for enabling the operator to bring the work-engaging face 44 of each abrasive wheel into a preselected, predetermined position with ease and precision. Referring to Figs. 3, 4 and 5, it will be perceived that this is accomplished by operatively associating with each of the wheels 34 an indicator capable of apprising the operator when the grinding face is located precisely in the desired position. Thus, in repositioning the wheels after a dressing operation, the indicator means 65 permits the operator to adjust the grinding heads until the grinding faces 44 of the wheels are precisely where they should be, rather than merely where the operator thinks they should be. In the present instance, the indicator means 85 comprises a pair of detectors 86 each operatively associated with a corresponding one of the abrasive wheels to define a reference plane for the predetermined position of its grinding face 44, together with a perceptible signal means 88' which may be electrically actuated. As indicated in Figs. 4 and 5, each of the detectors 86 comprises a resilient finger 89 of spring steel or the like terminating at its free end in a hardened tip 96 preferably of toolstock known in the trade as Carboloy. The finger 89 is supported by means of a bracket 9| and a relatively small diameter rod 92 which passes through a resilient bushing 94 in the bracket, the depending end of the rod 92 being mechanically fixed to the end of the finger 89. Disposed in overlying and supporting relation with the foregoing parts in each of the detectors 86 is a head 95 fixed to a sleeve 96. The latter is slidably housed in a bore 98 in the wheel protective housing 42 running substantially parallel to the rotational axis of the abrasive wheel. Adjustment of each detector 86 in a direction parallel to the rotational axis of the wheel is effected as by means of an adjusting knob 99 having a threaded stem. I66 which engages a tapped hole IOI in the housing 42. Mounted on the stem I66 for axial movement therewith as by means of collars I62, but relatively rotatable with respect to the stem, is an arm I64. The latter fits over the end of the sleeve 96 remote from the head 95 and may be fixed relative to the sleeve 96 by means of a set screw I65, the inner end of which tightly engages a groove I66 in the sleeve.

The finger 89 of each detector 86 may be shifted into or out of the path of axial movement of its associated abrasive wheel by the simple expedient of loosening the set screw I65 and rotating the detector assembly within the bore 98 which surrounds the sleeve 96. In order to permit the detector to remain in a given position of angular adjustment, there is associated with each of the sleeves 96 an appropriate friction drag. This may, for example, take the form of a springloaded plunger I68 mounted within a bore I69 in the housing 42, the tension of the loading spring II6 being regulated as by means of a closure plug III.

For the purpose of actuating the perceptible signal means 68 upon arrival of the grinding face 44 at its predetermined position, each of the detectors 86 is equipped with an interesting signalgenerating means. Since such means is substantially identical for each detector, a description of one will suflice for both. Turning again to Fig. 5, it will be perceived that the head 95 in the present instance has housed therein an acoustic pickup, preferably in the form of a crystal cartridge I I2 similar to the cartridge of a phonograph pickup. Clamped in the crystal cartridge H2 and leading downwardly therefrom is a "needle member H4 in the form of a relatively stiff but small diameter wire connected at its opposite end to the spool-like upper end I I5 of the rod 62. The latter and its point of connection with the needle member I I4 are surrounded by a resilient protectiveiaoet "Ht can nes *by ehon'ow bass m; which eonsftituies a es-feet the head as. Thwart-ridge ii": is chhneeted, preferably ioy means ef sliiel-ded wires H9, 1 20, to en'eiectr'ome ainfil-ifier l 2--l-. iec mistie impui-ses fine to ersntaet between the giihdih'g face 4'3 and the hardened tip on the iieteetoi finger are impressed 'iiboh the em t-ridge I The "qry'sth'leieinent Within the iatter geh erates smail -e1edtr-ma1 impi-iises 'i repoi tienal ts the hdoii'st'ib mpulses faihd these aie a tilifie'ti by fthe items H 1 vere'd as audible sound sy iieims ofai'oiitispeaker P22.

the opeiatibnof "the Iiiahi-ne ens the iiidialtihg mean 8-5 is no doubt eireaay appari *e'nt'to these ski'liedin the n, a brief synopsis tnereofmig vm 'hel-lifiil at this point. Assume, fifstbf: all, that the detedtois 8 5 inludirfg "the fingers 89 fhaire beenhdjiisted to de'fihethe p'refietei'mined lbcation for "eaeh of the grinding iecesfl ma that the'fingeis as are in th'epath hfriibi'r'einent "of their associ'atel abrasive Wheels. "A's's'fiime also that the d'fe'ssing operation has inst been completed and that the grinding heads 28 the wheels fl l' taireiTi t'hei-r'retreieted position, 5s "illustrated in Fig. 3. Considering first the Tight hand "one *ofthe grind-mg he'ads 2 s, will be appreciated that the head can 'be retraeted a sl ighvadtiiti'on'l'distance by *means of the aitiidt'qi :61 to piovide blealaneefbetwee'n the fst'o'ps'f'lla, -52 "anfl'th'e spac'er 68. "When this has beenione, the plunger "ti-and itsopei'ati-n'g knob 84 aie "piis he'ci inwardly to -the position indi- "cated "Fig. *1, swingin the spacer "63 down wa'rdly andiiito its 'inoperative*position. At this *poiiitfitheadtuatoi' 6| orthe biasing means ass'oia te'c i thefewith is pefmitte'l to-s hif-t the grind- 'iiighead 2a towers the guideba'rs *3, bringing the stops :9, 5*: into direct abutment with eeeh other. "By ceiffiiliy rotating *the hand wheel 60 alt the front of the-bed 22, "the ope'rator ro- "taite the stop *adjiis'tirig screw 54 93nd 62 1158 the step '"ilfito Tetfeait slowly in a-tiiree on anpmaem ing the work with the stop 49 fiiii'otv i'ifig it -in together with its =abi'asive "Wheel 34, toward the Work suflporting "g'uide hai's fl ht the-center df the inachi'ne;ea;using the gfindihg @206 E4 of the wheel to 'iip'p'roach its *preuetermmea mositibh.

*adiii'stiiig movement is continued-until initi'ltiiin "bf 'edht'alt between the "grinding f-a'c'e and the hardened "tip 90- f the-detector finihe *i'siiltirig "'alcbilstitil electrical-im- 'puises tine to *tniseoritact -eause the iou'ispealker 1 22 to *emit "a sudden --rauc'ous sound. At this s mm, *the e eretor back 0ft oh his aii jus'tnient over so slightly until this sound is reducedfto "a ldw' levl o'rfiisappears eiitirelygat whihpoint *th-e ie'sifed oi i justinent er the g'rindihg face M Will have been =alchiev'ed. -Th'e same sequence is, "of *cours'e, followed for positioning the leftgfi'ndihg head.

While tine might suppose that *co'nsiderabie WeaFwoifldocur on the tips flil ot the dtetito'r *fingersfBS as-they contact the *g'rindingTaces- M, "it has 'fin "T011116. that when Carbdldy tips "are "used, the Wear is negligible even though the "eontait with the rinding 'face -i's maintained -ove'r long periods of time. T-his probably due tio th'e faot that-each of the arms BB has co"n s"fderathiie resiliency and also to the fa'ot tha t "even the 'bar'est boliteiet betW-eeh theftip 32121 'the grinding fade is su-fii'eintito'piov iki a pdwei' fur-"Signal through' the speaker 1-22 lfmoweven, it ShbiiId b'e 'ifiSifw t0 'r o'ii-ik the dtedtors fis iii't'o B inoperative after the wheels smo -their faces 44 have piediselypositioned. this may readily be done by 186i screw 1135 and rotating the eeteeters 86 in the manner already outlined ah'o've. By pr'oper pr nortio'nir ig 0f the parts, such movement can be effeeted "without piistuibing the axial -'-adiiiistmex it o'i the eeteemrs ai demanded by the knobs The susceptibility er the indicating means 85 0 for use in =dtermin'ing the @mofint :remeveeirdm the grinding "iaize -ef either er -lalith @b'ras'ive wheel's :by a messing operation wiH he readily apparent 5mm the foregoing ciesei iption. may failitated by mountin 'h dalibrated Knot shown) adjacent 0f -the adjusting lmbb's 99 er in proximity to some other-movable pas'it 0f eah aetector -9e's'semb1y.

Upon re'fie'otibn, this itehisp'taibi'i-ity 0f the md-i ester means 8 5 'fdr the nutnmaitic xz'ciritrGH-ing 01 in'feed of eithernr' beth abrasive Wheels @111 who be apparent. For such purpo'se, the-amplifier and perceptibie signal means may be ooimeotefi to the control system of the qnatihine so a's tb reverse the feed end retui n the wheels when their igi inding fai'oes have sea-chad a. predetermined iiosi'tio'n. If desired, the -*si'g n'a1 may be eliminated completely m -iavor of a fiir'eet actuating connection between the amplifier 88 and ithe eijntidl system 1 (if the meehine.

IeIaiinas'my invention: r 1. A grinding mach'me mom-prising, in eombi "nation-a basep'a w'o'rksupport on said base a *paiir o'f "gt-"inning means-mounted -on' saia base for linear movement reiative -t0 th'e same and to said work siippoi't a pair-of abmsive wheels each i ourn'ajled in a, respeetive one o'f' saiti, grinding -hea'ds, each said wheel -respetiv1y an individual grinding fae'e thereon adiacent said "work support, iiiesm ineiud'ing -a'n adjustable stop interposed b'etwee'meach saiiderinfling head 1 and said base fo'r positioning said "iridivid ual grin'd-ing @ae'es welaitive to sa i'i woi k support, means fo'r nerm'allybiasing said grinding 'hea'ds tow'ard s'a ifi w'oi'k support sand a'l'ternativeiy rtra'tin'g s'a3idhe'ads from sam -support, an-detector s'iipl'riorted-on saiii' b'ase and' hiaa ing a. relatively flat -resil-ient finger disposed in the pzith bf sziii grinding faces for iiitereeption the'reo'f r'esponse to mo vemen't cif s'ziidQr-in'ding heads b'y 'setiti adjustz'ibie stop means, said finger being adapted to sense arnival of said grinding fac'es ir'it'o predetei mineli positi'ons rlaitive 't'o saiii -w'ofik support, 5 and mean's includ -ing a,'-=pe1deptih1e si'g-n9i1= dVioe mnneeted to -'s'a',i'd d'etetor, 'said signal deviee be'ingxsuscepti'ble 6f j proiuin'g "3, p'ereeptible Sigliil 'in respon'se to impulses f'I Om SaJd fiIi'gGr. V

J2. -Azg ninding m aschmelcomprismg the combination o'f ab'ase, work isuppo'ma'a minding tso heaid mourit'ed on-' said :base for axial movement t relative lte :siajid wofikfsupport and :tozss'aid ribas'e, nniabrasive element ijo'urnaleti iin fis'aid zgriniiing head and in'ovable laxially therewith, said iabra- -sive element leaving an Work-engaging suxface r flying-transversely bf thexdireetim ofiaxial m'owment 60f isfiid ,zgrindi-ng erhead, mn adj ustabie-fist'ap j-means associated with :said :grinding .:-hea'd .ior axial positioning mf ssa'id abrasive ielement, sand tits tworkeengaging asurface trelative ito ss'aidxwork support, means ifor surging :said :igrinding :hea'd against said :a'djust'abie .zstop emeans, ea idete'ctor fhaving 5a rrelatively -fiat resilient finger ewith ta h ardened metallic'itipztorisensing zarrival-iofssaid -workeengaging surface into 3a. predetermined 77 axiaispos'ition relativ e to said work support response to adjustment of said step means, said resilient finger being disposed transversely of .the direction of axial movement of said grinding head, and means including a perceptible signal device connected to said detector, said signal device being susceptible of producing a perceptible signal upon arrival of said work-engaging surface in said predetermined position.

3. A grinding machine comprising the combination of a base, a pair of abrasive wheels mounted onsaid base and susceptible of relative linear movement toward and away from each other, said wheels having opposed grinding faces, means'for adjusting the positions of said abrasive wheels relative to each other, detector means interposed between said abrasive wheels and mounted in close proximity to their respective grinding faces for interception of the same during relative linear adjustment of said. Wheels, and. a perceptible signal means connected to said detector means for actuation by the latter upon arrival of said grinding faces in a predetermined relative position.

. 4. A grinding machine comprising the combination of a base, a work support, a pair of abrasive wheels mounted on said base in strad dling relation with said work support and susceptible of relative axial movement toward and away from said support, said wheels having p-- posed grinding faces, means for adjustably positioning said abrasive wheels and their grinding faces relative to said work support and to each other, detectors interposed between said abrasive wheels and including means for sensing arrival of their respective grinding faces in predeter mined positions during relative axial adjustment of said wheels, and means including a perceptible signal device connected to said detectors for actuation by the latter upon arrival of said grinding faces in said predetermined positions.

5. In a grinding machine, the combination comprising a base, a pair of abrasive wheels having opposed grinding faces and mounted in spaced apart relation on said base, guide means interposed between said grinding faces for channeling workpieces therebetween, a pair of grinding heads for rotatably supporting said abrasive wheels, a pair of beds on said base adapted to support respective ones of said grinding heads and their associated wheels for relative linear movement toward and away from each other as well as toward and away from said guide means, means including an adjustable stop interposed between each said grinding head and its associated bed for positioning a corresponding one of said grinding faces, a pair of detectors supported upon said base and respectively associated with a corresponding one of said abrasive wheels, means including a relatively fiat finger carried by each said detector and disposed between said abrasive wheels for interception of an associated one of said grinding faces in response to adjustment of a corresponding one of said grinding heads, each said finger being adapted to sense arrival of the grinding face into a predetermined position relative to said guide means, and means including an electrically actuated perceptible signal device connected to said detectors, said signal device being susceptible of producing a perceptible signal in response to impulses from said finger means. 7

6. An indicator for use with a grinding machine having an adjustably positionable abrasive wheel with a work-engaging face thereon, said indicator comprising the combination of a sup- 10 porting member attachable to said machine, a head on said supporting member, an acoustic pick-up protectively enclosed within said head, a signal amplifying device connected with said pick-up, means connected with said amplifying device for producing a perceptible signalin response to mechanical impulses on said acoustic pick-up, a finger disposed for interception of the work-engaging face ofthe abrasive wheel asan incident to adjustment of the same, and a resiliently mounted rod connected between said finger and said pick-up for transmission of mechanical impulses thereto.

7. An indicator for apprising a grinding machine operator as to the position of the workengaging face of an abrasive wheel, said wheel being adjustable relative to said machine, said indicator comprising the combination of a supporting member attachable to said machine, a head on said supporting member, an acoustic pick-up within said head, a bracket depending from said head, a resilient fingersupported by said bracket and adapted for interception of the workengaging face of said wheel as an .incident to adjustment of the same, means supported by said bracket and connecting said finger with said pick-up, a signal amplifier connected with said pick-up, and means connected to said amplifier for producing a perceptible signal in response to mechanical impulses on said pick-up due .to contact between said finger and the work-engaging face of said wheel.

8. An indicator for apprising a grinding machine operator as to the position of the grinding face of an abrasive wheel, said indicator comprising the combination of a supporting member, means for adjusting said supporting member relative to said machine and the grinding face of the abrasive wheel, an acoustic pick-up mounted on said supporting member, a bracket carried by said member, a resilient finger carried by said bracket for interception of said grinding face, means connecting said finger with said pick-up, a signal amplifier connected with said pick-up, perceptible signal means connected to said amplifier, and a mechanical connection on said bracket and interposed between said finger and said pick-up.

9. An indicator for apprising an operator as to the position of the grinding face of an abrasive wheel, said wheel being adjustable relative to said machine, said indicator comprising, in combination, a hollow supporting sleeve attachable to said machine, a head fixed to said sleeve, means for effecting linear adjustment of said sleeve and head along an axis substantially parallel with the direction of adjustment of the abrasive wheel, means for effecting angular adjustment of said sleeve and head about its linear adjustment axis, an acoustic pick-up in said head, a bracket depending from said sleeve, a resilient finger supported by said bracket and disposable into intercepting relation with the grinding face of the abrasive wheel, a hardened tip on said finger, a rod member carried by said bracket and interposed between said finger and said. pick-up, an electronic amplifier connected to said pick-up via conductors housed within said sleeve, and a loudspeaker connected to said amplifier for reproducing amplified acoustic impulses resulting from interception of said grind ing face by the tip on said finger.

10. The combination of a grinding machine having a pair of closely spaced abrasive wheels and means disposed therebetween for supporting a workpiece, with anindicator means comprising a pair of detectors interposed between said wheels and disposed for interception of respective ones of, their grinding faces when the latter are ina predetermined position relative to the workpiece supporting means, and means including a perceptible signaling device associated with and susceptible of actuation by said detectors.

11. The combination of a grinding machine having a pair of closely spaced abrasive wheels and means disposed therebetween for supporting workpieces, with an indicator means comprising a pair of supporting members attachable to said machine, an acoustic pick-up carried by each of said supporting members, a pair of relatively fiat fingers each-mounted on a respective one of said supporting members, said fingers being interposedbetween said abrasive Wheels and disposed for interception of respective ones of their grinding faces when the latter are in predetermined positions relative to the workpiece supporting means, an amplifying device connected to each saidacoustic pick-up, a perceptible signal device connected to said amplifier, and means connecting respective ones of said fingers with corresponding ones of said acoustic pick-ups.

, 12. The combination of a grinding machine having a pair of spaced apart enclosed abrasive wheels and a pair of vertically spaced guide bars therebetween for channeling workpieces past the opposed grinding faces of said wheels, with a 12 grinding face position indicator comprising a pair of supporting members adjustably attachable to the enclosure for the abrasive wheels, ahead on each of said adjusting members, an acoustic pick-up housed within each said head, a pair of resilient fingers disposed for interception of respective ones of the grinding faces when the same are in predetermined position relative to' the guide bars, means supporting respective ones 01' said fingers from corresponding ones of said heads, connecting members interposed between each of said fingers and a corresponding one oi said acoustic pick-ups, an amplifier associated with and connected to each said acoustic pickup, and a loudspeaker connected to said amplifier for reproducing amplified acoustic impulses resulting from contact between said fingers and their associated grinding faces. 7

RALPH D. GARDNER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,638,028 Gardner Aug. 9, 1927 1,891,777 Plimmer Dec. 20, 1932 1,961,849 Fraser June 5, 1934 2,087,662 Bysshe et al July 20,193! 2,142,444 Hall Jan. 3, 1939 2,209,711 Young July 30, 1940 

